1. Field of the Invention
This invention relates generally to a novel method and composition of matter, and more particularly to a novel method for the direct growth of 3D micro/nanostructures that have the capacity to reduce light reflection while enhancing absorption efficiency. In one embodiment, by the method of this invention, vertical cone-shaped pillars of Ge are directly formed on a wide range of substrates, the formed nanoneedle (NN) arrays offering a gradually reducing effective refractive index of the material from the bottom to the top.
2. Brief Description of the Related Art
To achieve more efficient approaches to absorption of light, exploration of novel three-dimensional structures with relevant material systems has been undertaken. For instance, in the case of 3D micro/nanostructures, they have been shown to reduce light reflection while enhancing the absorption efficiency. Vertical cone-shaped pillars are attractive in this regard due to the gradual reduction of the effective refractive index of the material from the bottom to the top. Based on this concept, black Si has been demonstrated in the past by utilizing various processes, including femto-second laser bombardment or patterned etching of the surface of bulk silicon and thin film (TF) substrates. Black Si has been widely explored for photovoltaic and photodiode applications. Due to its smaller bandgap and unique optical properties, germanium (Ge) planar and non-planar structures have also been widely studied for infrared photodetector and photodiode applications. What is needed for Ge, still is a simple and efficient method for growing Ge cone shaped structures, the method also suitable for the growth of such structures on a number of types of substrates.